1. Field of Invention
The invention relates to a card edge connector and, in particular to a card edge connector with a position guider. The card edge connector can be used on a mother board of an electronic device for electrically connecting with a daughter board.
2. Related Art
The conventional card edge connector is normally comprised of a connection part, at least one position guider, and a fixing device. The connection part is provided with several terminals for electrical contacts with the contacts on the inserted daughter board. The position guider prevents incorrect insertion of the daughter board. The fixing device fixes the card edge connector on the circuit board.
In light of technological advances and environmental protection, all devices are made smaller. Therefore, the card edge connector and daughter boards have to be reduced in size too. The gaps between the terminals inside the card edge connector and the gaps between the contacts on the daughter board have to be reduced too.
Take a conventional card edge connector and a daughter board as an example. The width of each terminal inside the card edge connector is about 0.2 mm. The terminals are disposed at a pitch of 0.5 mm. Thus, the gap between each two adjacent terminals is 0.3 mm. Normally, the allowed error for a position guider is ±0.1 mm. The width of each connecting point on the daughter board is 0.33 mm. If they are disposed at the same pitch of 0.5 mm, the gap between each two adjacent contacts is 0.27 mm.
As shown in FIGS. 1A and 1B, the ideal matching between a card edge connector and a daughter board happens when there is no misalignment shift. The middle line of the crack 420 on the daughter board aligns with the middle of the position guider 200 of the card edge connector. Therefore, the middle line of the terminal 310 can align with the middle line of the connecting point 410 on the daughter board. Each terminal 310 inside the connection part 300 thus aligns well with each connecting point 410 on the daughter board 400, forming a good electrical connection.
As shown in FIGS. 1C and 1D, even though each of the card edge connector and the daughter board are satisfactory in measures, accumulated tolerance may result in mismatching or difficulty in practical uses. For example, suppose the left side of the position guider 200 of the card edge connector has an error of −0.1 mm and the left width of the crack 420 has an error of +0.05 mm. If the left side of the position guider 200 aligns with the left side of the daughter board crack 420 (their middle lines misalign with each other), then the misalignment shift between them is 0.15 mm when the daughter board 400 is inserted. The middle line of the terminal 310 misaligns with the middle line of the connecting point 410 by 0.15 mm. Therefore, the terminal 310 misaligns with the connecting point 410, contacting with each other by a tiny area. This will result in unstable electrical connections. Moreover, there is a tolerance between two adjacent contacts 410 on the daughter board. When accumulated tolerance happens, the accumulated misalignments of the contacts 410 and terminals 310 far from the base line will be big. This may eventually result in no conduction between a terminal 310 and a connecting point 410 or a short circuit because one terminal 310 simultaneously overlaps with two contacts 410. This is more likely to happen when the terminals 310 and the contacts 410 have a fine pitch or high density.
In FIGS. 1C and 1D, the gap between the left side of the position guider 200 and the left side of the daughter board crack 420 is to ensure the positions and shapes of the position guider 200 and the daughter board crack 420. In practice, the left side of the position guider 200 and the left side of the daughter board crack 420 stick to the same plane with no gap.
Moreover, since there is a gap between the daughter board crack 420 and the position guider 200 of the card edge connector due to the tolerance, vibrations or any other external forces may result in relative horizontal shifts between them when the daughter board 400 is inserted into the connection part 300 of the card edge connector. Therefore, the terminals 310 and the contacts 410 have a misalignment shift that causes imperfect contacts or short circuits.